Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. For example, processing circuitry decodes prediction information of a current block in a current picture from a coded video bitstream. The prediction information is indicative of an affine merge mode with offset. Then, the processing circuitry decodes, from the coded video bitstream, a set of offset parameters that is used to determine a motion vector difference, and applies the motion vector difference to first motion vectors of multiple control points of a base predictor of the current block to determine second motion vectors at corresponding multiple control points of the current block. Further, the processing circuitry determines parameters of an affine model based on the second motion vectors at the corresponding multiple control points of the current block, and reconstructs at least a sample of the current block according to the affine model.

INCORPORATION BY REFERENCE

This application is a continuation of U.S. application Ser. No.16/503,451, filed Jul. 3, 2019, which claims the benefit of priority toU.S. Provisional Application No. 62/741,532, “METHODS OF AFFINE MOTIONMODEL CODING WITH PREDICTION OFFSETS” filed on Oct. 4, 2018, the entirecontents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1, a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes receiving circuitry and processing circuitry. For example, theprocessing circuitry decodes prediction information of a current blockin a current picture from a coded video bitstream. The predictioninformation is indicative of an affine merge mode with offset. Then, theprocessing circuitry decodes, from the coded video bitstream, a set ofoffset parameters that is used to determine a motion vector difference,and applies the motion vector difference to first motion vectors ofmultiple control points of a base predictor of the current block todetermine second motion vectors at corresponding multiple control pointsof the current block. Further, the processing circuitry determinesparameters of an affine model based on the second motion vectors at thecorresponding multiple control points of the current block, andreconstructs at least a sample of the current block according to theaffine model.

In some embodiments, the processing circuitry decodes, from the codedvideo bitstream, an offset distance index and an offset direction indexthat are used to determine the motion vector difference, and determinean offset distance according to the offset distance index and apre-defined mapping of offset distance indices and offset distances.Then, the processing circuitry determines an offset direction accordingto the offset direction index and a pre-defined mapping of offsetdirection indices and offset directions.

In an example, the processing circuitry applies the motion vectordifference to two control points of the base predictor when afour-parameter affine model is used. In another example, the processingcircuitry applies the motion vector difference to three control pointsof the base predictor when a six-parameter affine model is used.

in an embodiment, the processing circuitry applies the motion vectordifference to the first motion vectors that refer to a first referencepicture to determine the second motion vectors for the first referencepicture, and applies a mirror of the motion vector difference to thirdmotion vectors of the control points of the base predictor that refer toa second reference picture to determine fourth motion vectors at thecorresponding multiple control points of the current block that refer tothe second reference picture.

In another embodiment, the processing circuitry applies the motionvector difference to the first motion vectors that refer to a firstreference picture to determine the second motion vectors that refer tothe first reference picture, and applies a mirror of the motion vectordifference to third motion vectors of the control points of the basepredictor that refer to a second reference picture to determine fourthmotion vectors at the corresponding multiple control points of thecurrent block that refer to the second reference picture when the secondreference picture is on an opposite side of the current picture from thefirst reference picture.

In some examples, the processing circuitry applies the motion vectordifference to the first motion vectors that refer to a first referencepicture to determine the second motion vectors that refer to the firstreference picture, and calculates a scaling factor based on a firstpicture number difference of the first reference picture and the currentpicture and a second picture number difference of a second referencepicture and the current picture. Further, the processing circuitryapplies the motion vector difference that is scaled according to thescaling factor to third motion vectors of the control points of the basepredictor that refer to the second reference picture to determine fourthmotion vectors at the corresponding multiple control points of thecurrent block that refer to the second reference picture.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 shows an example of spatial and temporal candidates in someexamples.

FIG. 9 shows examples for UMVE according to an embodiment of thedisclosure.

FIG. 10 shows examples for UMVE according to an embodiment of thedisclosure.

FIG. 11 shows an example of a block with an affine motion model.

FIG. 12 shows examples of affine transformation according to someembodiments of the disclosure.

FIG. 13 shows a plot that illustrates control points CP0 and CP1 for acurrent block.

FIG. 14 shows a flow chart outlining a process example according to someembodiments of the disclosure.

FIG. 15 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304)(or coded video bitstreams), can be processed byan electronic device (320) that includes a video encoder (303) coupledto the video source (301). The video encoder (303) can include hardware,software, or a combination thereof to enable or implement aspects of thedisclosed subject matter as described in more detail below. The encodedvideo data (304) (or encoded video bitstream (304)), depicted as a thinline to emphasize the lower data volume when compared to the stream ofvideo pictures (302), can be stored on a streaming server (305) forfuture use. One or more streaming client subsystems, such as clientsubsystems (306) and (308) in FIG. 3 can access the streaming server(305) to retrieve copies (307) and (309) of the encoded video data(304). A client subsystem (306) can include a video decoder (310), forexample, in an electronic device (330). The video decoder (310) decodesthe incoming copy (307) of the encoded video data and creates anoutgoing stream of video pictures (311) that can be rendered on adisplay (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). Instill others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412)(e.g., a display screen) that is not an integral partof the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo 1I compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540)(e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. Ina videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771)(data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

Aspects of the disclosure provide techniques to simplify affine motioncompensation with prediction offsets.

Generally, a motion vector for a block can be coded either in anexplicit way, to signal the difference to a motion vector predictor(e.g., advanced motion vector prediction or AMVP mode); or in animplicit way, to be indicated completely from one previously coded orgenerated motion vector. The later one is referred to as merge mode,meaning the current block is merged into a previously coded block byusing its motion information.

Both merge mode and the AMVP mode construct candidate list duringdecoding.

FIG. 8 shows an example of spatial and temporal candidates in someexamples.

For the merge mode in the inter prediction, merge candidates in acandidate list are primarily formed by checking motion information fromeither spatial or temporal neighboring blocks of the current block. Inthe FIG. 8 example, candidate blocks A1, B1, B0, A0 and B2 aresequentially checked. When any of the candidate blocks are validcandidates, for example, are coded with motion vectors, then, the motioninformation of the valid candidate blocks can be added into the mergecandidate list. Some pruning operation is performed to make sureduplicated candidates will not be put into the list again. The candidateblocks A1, B1, B0, A0 and B2 are adjacent to corners of the currentblock, and are referred to as corner candidates.

After spatial candidates, temporal candidates are also checked into themerge candidate list. In some examples, the current block's co-locatedblock in a specified reference picture is found. The motion informationat C0 position (bottom right corner of the current block) of theco-located block will be used as temporal merge candidate. If the blockat this position is not coded in inter mode or not available, C1position (at the outer bottom right corner of the center of theco-located block) will be used instead. The present disclosure providestechniques to further improve merge mode.

The advanced motion vector prediction (AMVP) mode in HEVC refers tousing spatial and temporal neighboring blocks' motion information topredict the motion information of the current block, while theprediction residue is further coded. Examples of spatial and temporalneighboring candidates are shown in FIG. 8 as well.

In some embodiments, in AMVP mode, a two-candidate motion vectorpredictor list is formed. For example, the list includes a firstcandidate predictor and a second candidate predictor. The firstcandidate predictor is from the first available motion vector from theleft edge, in the order of spatial A0, A1 positions. The secondcandidate predictor is from the first available motion vector from thetop edge, in the order of spatial B0, B1 and B2 positions. If no validmotion vector can be found from the checked locations for either theleft edge or the top edge, no candidate will be filled in the list. Ifthe two available candidates are the same, only one will be kept in thelist. If the list is not full (with two different candidates), thetemporal co-located motion vector (after scaling) from C0 location willbe used as another candidate. If motion information at C0 location isnot available, location C1 will be used instead.

In some examples, if there are still no enough motion vector predictorcandidates, zero motion vector will be used to fill up the list.

In some embodiments, prediction offsets can be signaled on top ofexisting merge candidates. For example, a technique that is referred toas ultimate motion vector expression (UMVE) uses a special merge mode inwhich an offset (both magnitude and direction) on top of the existingmerge candidates is signaled. In this technique, a few syntax elements,such as a prediction direction IDX, a base candidate IDX, a distanceIDX, a search direction IDX, and the like, are signaled to describe suchan offset. For example, the prediction direction IDX is used to indicatewhich of the prediction directions (temporal prediction direction, e.g.,L0 reference direction, L1 reference direction or L0 and L1 referencedirections) is used for UMVE mode. The base candidate IDX is used toindicate which of the existing merge candidates is used as the startpoint (base candidate) to apply the offset. The distance IDX is used toindicate how large the offset is from the starting point (along x or ydirection, but not both). The offset magnitude is chosen from a fixnumber of selections. The search direction IDX is used to indicate thedirection (x or y, + or − direction) to apply the offset.

In an example, assuming the starting point MV is MV_S, the offset isMV_offset. Then the final MV predictor will be MV_final=MV_S+MV_offset.

FIG. 9 shows examples for UMVE according to an embodiment of thedisclosure. In an example, the starting point MV is shown by (911) (forexample according to the prediction direction IDX and base candidateIDX), the offset is shown by (912) (for example according to thedistance IDX and the search direction IDX), and the final MV predictoris shown by (913) in FIG. 9. In another example, the starting point MVis shown by (921)(for example according to the prediction direction IDXand base candidate IDX), the offset is shown by (922) (for exampleaccording to the distance IDX and the search direction IDX), and thefinal MV predictor is shown by 923 in FIG. 9.

FIG. 10 shows examples for UMVE according to an embodiment of thedisclosure. For example, the starting point MV is shown by (1011) (forexample according to the prediction direction IDX and base candidateIDX). In the FIG. 10 example, 4 search directions, such as +Y, −Y, +Xand −X, are used, and the four search directions can be indexed by 0, 1,2, 3. The distance can be indexed by 0 (0 distance to the starting pointMV), 1 (1 s to the starting point MV), 2 (2 s to the starting point MV),3 (3 s to the starting point), and the like. Thus, when the searchdirection IDX is 3, and the distance IDX is 2, the final MV predictor isshown as 1015.

In another example, the search direction and the distance can becombined for indexing. For example, the starting point MV is shown by(1021) (for example according to the prediction direction IDX and basecandidate IDX). The search direction and the distance are combined to beindexed by 0-12 as shown in FIG. 10.

According to an aspect of the disclosure, affine motion compensation, bydescribing a 6-parameter (or a simplified 4-parameter) affine model fora coding block, can efficiently predict the motion information forsamples within the current block. More specifically, in an affine codedor described coding block, different part of the samples can havedifferent motion vectors. The basic unit to have a motion vector in anaffine coded or described block is referred to as a sub-block. The sizeof a sub-block can be as small as 1 sample only; and can be as large asthe size of current block.

When an affine mode is determined, for each sample in the current block,its motion vector (relative to the targeted reference picture) can bederived using such a model (e.g., 6 parameter affine motion model or 4parameter affine motion model). In order to reduce implementationcomplexity, affine motion compensation is performed on a sub-blockbasis, instead of on a sample basis. That means, each sub-block willderive its motion vector and for samples in each sub-block, the motionvector is the same. A specific location of each sub-block is assumed,such as the top-left or the center point of the sub-block, to be therepresentative location. In one example, such a sub-block size contains4×4 samples.

In general, an affine motion model has 6 parameters to describe themotion information of a block. After the affine transformation, arectangular block will become a parallelogram. In an example, the 6parameters of an affine coded block can be represented by 3 motionvectors at three different locations of the block.

FIG. 11 shows an example of a block (1100) with an affine motion model.The block (100) uses motion vectors {right arrow over (v₀)}, {rightarrow over (v₁)}, and {right arrow over (v₂)} at three corner locationsA, B and C to describe the motion information of the affine motion modelused for the block (1100). These locations A, B and C are referred to ascontrol points.

In a simplified example, an affine motion model uses 4 parameters todescribe the motion information of a block based on an assumption thatafter the affine transformation, the shape of the block does not change.Therefore, a rectangular block will remain a rectangular and same aspectratio (e.g., height/width) after the transformation. The affine motionmodel of such a block can be represented by two motion vectors at twodifferent locations, such as at corner locations A and B.

FIG. 12 shows examples of affine transformation for a 6-parameter affinemode (using 6-parameter affine model) and a 4-parameter affine mode(using 4-parameter affine model).

In an example, when assumptions are made such that the object only haszooming and translational motions, or the object only has rotation andtranslation models, then the affine motion model can be furthersimplified to a 3-parameter affine motion model with 2 parameters toindicate the translational part and 1 parameter to indicate either ascaling factor for zooming or an angular factor for rotation.

According to an aspect of the disclosure, when affine motioncompensation is used, two signaling techniques can be used. The twosignaling techniques are referred to as a merge mode based signalingtechnique and a residue (AMVP) mode based signaling technique.

For the merge mode based signaling technique, the affine information ofthe current block is predicted from previously affine coded blocks. Inone method, the current block is assumed to be in the same affine objectas the reference block, so that the MVs at the control points of thecurrent block can be derived from the reference block's model. The MVsat the current block' other locations are just linearly modified in thesame way as from one control point to another in the reference block.This method is referred to as model based affine prediction. In anothermethod, neighboring blocks' motion vectors are used directly as themotion vectors at current block's control points. Then motion vectors atthe rest of the block are generated using the information from thecontrol points. This method is referred as control point based affineprediction. In either method, no residue components of the MVs atcurrent block are to be signaled. In other words, the residue componentsof the MVs are assumed to be zero.

For the residue (AMVP) mode based signaling technique, affineparameters, or the MVs at the control points of the current block, areto be predicted. Because there are more than one motion vectors to bepredicted, the candidate list for motion vectors at all control pointsis organized in grouped way such that each candidate in the listincludes a set of motion vector predictors for all control points. Forexample, candidate 1={predictor for control point A, predictor forcontrol point B, predictor for control point C}; candidate 2={predictorfor control point A, predictor for control point B, predictor forcontrol point C}, etc. The predictor for the same control point indifferent candidates can be the same or different. The motion vectorpredictor flag (mvp_l0_flag for List 0 or mvp_l1_flag for List 1) willbe used to indicate which candidate from the list is chosen. Afterprediction, the residue part of the parameter, or the differences of theactual MVs to the MV predictors at the control points, are to besignaled. The MV predictor at each control point can also come frommodel based affine prediction from one of its neighbors, and the methoddescribed from the above description for affine merge mode can be used.

In some related methods, affine parameters for a block can be eitherpurely derived from neighboring block's affine model or control points'MV predictor, or from explicitly signal the MV differences at thecontrol points. However, in many cases the non-translational part of theaffine parameters is very close to zero. Using unrestricted MVdifference coding to signal the affine parameters has redundancy.

Aspects of the disclosure provide new techniques to better represent theaffine motion parameters therefore improve coding efficiency of affinemotion compensation. More specifically, to predict affine modelparameters in a more efficient way, the translational parameters of ablock are represented using a motion vector prediction, in the same wayor similar way as that is for a regular inter prediction coded block.For example, the translational parameters can be indicated from a mergecandidate. For the non-translational part, a few typically usedparameters such as rotation parameter and zooming parameter arepre-determined with a set of fixed offset values. These values areconsidered as some refinements or offset around the default value. Theencoder can evaluate the best option from these values and signal theindex of the choice to the decoder. The decoder then restores the affinemodel parameters using 1) the decoded translational motion vector and 2)the index of the chosen non-translational parameters.

In the following description, 4-parameter affine model is used as anexample, the methods described in the following description can beextended to other motion models, or affine models with different numbersof parameters as well, such as 6-parameter affine model, and the like.In some of the following description, the model used may not be alwaysaffine model, but possibly other types of motion model.

In an example, a 4-parameter affine model is described, such as shown byEq. 1

$\begin{matrix}\left\{ \begin{matrix}{x^{\prime} = {{\rho\;\cos\;{\theta \cdot x}} + {\rho\;\sin\;{\theta \cdot y}} + c}} \\{y^{\prime} = {{{- \rho}\;\sin\;{\theta \cdot x}} + {\rho\;\cos\;{\theta \cdot y}} + f}}\end{matrix} \right. & \left( {{Eq}.\mspace{14mu} 1} \right)\end{matrix}$where ρ is the scaling factor for zooming, θ is the angular factor forrotation, and (c, f) is the motion vector to describe the translationalmotion. (x, y) is a pixel location in the current picture, (x′, y′) is acorresponding pixel location in the reference picture.

Let a=ρcos θ, and b=ρ sin θ, Eq. 1 may become the following form as inEq. 2

$\begin{matrix}\left\{ \begin{matrix}{x^{\prime} = {{a \cdot x} + {b \cdot y} + c}} \\{y^{\prime} = {{{- b} \cdot x} + {a \cdot y} + f}}\end{matrix} \right. & \left( {{Eq}.\mspace{14mu} 2} \right)\end{matrix}$Thus, a 4-parameter affine model can be represented by a set ofmodel-based parameters {ρ, θ, c, f}, or {a, b, c, f}.

From Eq. 2, the motion vector (MV_(x), MV_(y)) at pixel position (x, y)may be described as in Eq. 3,

$\begin{matrix}\left\{ \begin{matrix}{{MV}_{x} = {{x^{\prime} - x} = {{a^{\prime}x} + {by} + c}}} \\{{MV}_{y} = {{y^{\prime} - y} = {{- {bx}} + {a^{\prime}y} + f}}}\end{matrix} \right. & \left( {{Eq}.\mspace{14mu} 3} \right)\end{matrix}$Where a′ is equal to (a−1), MV_(x) is the horizontal motion vectorvalue, and MV_(y) is the vertical motion vector value.

In some examples, the 4-parameter affine model can also be representedby the motion vectors of two control points, CP0 and CP1, of the block.Similarly, three control points may be required to represent a6-parameter affine model.

FIG. 13 shows a plot that illustrates control points CP0 and CP1 for acurrent block.

Using two control points CP0 and CP1, the motion vector at position (x,y) in the current block can be derived using Eq. 4:

$\begin{matrix}\left\{ \begin{matrix}{v_{s} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}x} - {\frac{\left( {v_{1y} - v_{0y}} \right)}{w}y} + v_{0x}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{w}x} + {\frac{\left( {v_{1x} - v_{0x}} \right)}{w}y} + v_{0y}}}\end{matrix} \right. & \left( {{Eq}.\mspace{14mu} 4} \right)\end{matrix}$where (v_(0x), v_(0y)) is motion vector of the top-left corner controlpoint CP0 as depicted in FIG. 13, and (v_(1x), v_(1y)) is motion vectorof the top-right corner control point CP1 as depicted in FIG. 13. In theexample of control-point based model, the affine model of the block maybe represented by {v_(0x), v_(0y), v_(1x), v_(1y)}.

In some related examples, affine parameters for a block can be eitherpurely derived from neighboring block's affine model or control points'MV predictor, or from explicitly signaling of the MV differences at thecontrol points. However, in many cases the non-translational part of theaffine parameters is very close to zero. Using unrestricted MVdifference coding to signal the affine parameters has redundancy. Newtechniques to better represent the affine motion parameters aredeveloped to improve coding efficiency.

Aspects of the disclosure provide techniques for improving codingefficiency of affine merge and affine motion vector coding. Thetechniques may be used in advanced video codec to improve the codingperformance of affine inter prediction. The motion vector hem may referto block mode (conventional motion vector where one whole block uses aset of motion information), such as the merge candidates in HEVCstandard. The motion vector here may also refer to sub-block mode (fordifferent parts of the block, different sets of motion information mayapply), such as affine mode and advanced temporal MV prediction (ATMVP)in VVC.

It is noted that the proposed methods may be used separately or combinedin any order. In the following description, the term block may beinterpreted as a prediction block, a coding block, or a coding unit,i.e. CU. It is proposed to predict current block's affine model based oncontrol point motion vectors (CPMVs) at 2 or 3 corners. After the CPMVsare predicted using model-based affine merge prediction or constructedcontrol-point based affine merge prediction, an available affine mergecandidate may be selected as the base predictor.

In some embodiments, a flag, such as an affine_merge_with_offset usageflag, is signaled to indicate whether the proposed method is used. Whenthe affine_merge_with_offset usage flag is indicative of using theproposed method, the number of base predictor candidates (e.g., thenumber of affine merge candidates) to be selected from may be determinedbased on a pre-defined value or a signaled value. In an example, thenumber of base predictor candidates is a predefined default value thatis known and then used by both encoder and decoder. In another example,the encoder side determines the number of base predictor candidates andsignals the number of base predictor candidates in the coded videobitstream, such as, but not limited to, in sequence parameter set (SPS),picture parameter set (PPS), or slice header.

In an example, when the number of base predictor candidate is 1, thebase predictor index is not signaled in the coded video bitstream, andthe first available affine merge candidate is used as the basepredictor. When the number of base predictor candidates is greater than1, the base predictor index is signaled in the coded video bitstream toindicate which affine merge candidate to be used as the base predictor.

After the base predictor is determined, CPMV values of the basepredictor may be used as starting point, and distance offset values maybe added on top of CPMV values to generate current block's CPMV values.

The offset values may be determined by the offset parameters. In someexamples, an offset parameter is provided in a form of offset directionindex and offset distance index. For example, the offset direction indexis signaled to indicate on which component(s) the offset may be appliedto a CPMV. It may be on CPMV's horizontal and/or vertical direction. Inan embodiment, there may be 4 offset directions for each control pointas shown below in Table 1, where only x or y direction has MVdifference, but not on both directions:

TABLE 1 Mapping of Offset Direction IDXs to Offset Directions OffsetDirection IDX 00 01 10 11 x-axis +1 −1 0 0 y-axis 0 0 +1 −1

In another embodiment, there's no limitation of only x or y has MVdifference, then the table for offset direction IDX may become as shownin Table 2, one of the eight offset directions may be used:

TABLE 2 Mapping of Offset Direction IDXs to Offset Directions OffsetDirection IDX 000 001 010 011 100 101 110 111 x-axis +1 −1  0  0 +1 −1+1 −1 y-axis  0  0 +1 −1 +1 −1 −1 +1

The offset distance index is signaled to indicate the magnitude ofoffset distance to be applied on the CPMV. In an example, the offsetdistance index is signaled in the form of pixel distance. In someembodiments, an offset distance table is used, and each offset distanceindex is mapped to offset distance in number of pixels according to theoffset distance table. The offset distance value may be integer orfractional values. The offset distance value indicates that the offsetto be applied to the base predictor's motion vector value.

In one example, a offset distance table with size of 4 is as shown inTable 3. The offset distance values in the table are {½, 1, 2, 4}, interms of pixels.

TABLE 3 Mapping of Offset Distance IDXs to Offset Distances OffsetDistance IDX 0 1 2 3 Offset 1/2- 1- 2- 4- Distance sample sample samplesample

In another example, an offset distance table with size of 5 is as shownin the Table 4. The offset distance values in the table are {½, 1, 2, 4,8}, in terms of pixels.

TABLE 4 Mapping of Offset Distance IDXs to Offset Distances OffsetDistance IDX 0 1 2 3 4 Offset ½- 1- 2- 4- 8- Distance sample samplesample sample sample

In another example, the mapping of offset distance values with 8 indicesis shown in Table 5. The offset distance values are in range of ¼ pixelsto 32 pixels.

TABLE 5 Mapping of Offset Distance IDXs to Offset Distances OffsetDistance IDX 0 1 2 3 4 5 6 7 Offset 1/4- 1/2- 1- 2- 4- 8- 16- 32-Distance sam- sam- sam- sam- sample sample sample sample ple ple ple ple

The number of distance indices and/or the value of pixel distancecorresponding to each distance index may have different values indifferent ranges, they are not limited by the aforementioned examples.

In an embodiment, the offset direction index and the offset distanceindex may be signaled only once for all control points, and the sameoffset distance may be applied to all CPMVs on the same offsetdirection.

In another embodiment, the offset direction index and the offsetdistance index parameters may be signaled for each control pointseparately. Each CPMV has a corresponding offset magnitude applied on acorresponding offset direction.

In some embodiments, when offset parameters are signaled for eachcontrol point, a zero_MVD flag may be signaled before offset parametersto indicate whether the motion vector difference is zero for thecorresponding CPMV. When the zero_MVD flag is true, in an example,offset parameters are not signaled for the corresponding CPMV. In anembodiment, when N control points are available (N is a positiveinteger), and the first N−1 control points have zero_MVD flags that aretrue, the last control point's zero_MVD may be inferred to be false, sothat its zero_MVD flag for the last control point is not signaled.

In another embodiment, when one set of offset parameters is signaled forall control points, zero_MVD flag may not be signaled.

Aspects of the disclosure provide techniques to signal offsetparameters.

In an embodiment, each control point has its offset parameters signaledseparately. In an example, the current block's merge flag andaffine_merge_with_offset usage flag are both true. When more than onepredictor candidates are existed to be potentially used for basepredictor, base predictor index is signaled from the encoder side to thedecoder side in an example. In another example, no base predictor indexis signaled, and predefined base predictor index can be used on theencoder side and the decoder side.

Further, for each control point (CP) of current block, Zero_MVD flag issignaled for the CP. When the CP is the last CP of the block, and allother CPs have Zero_MVD equal to 1 (true), Zero_MVD flag for the last CPis inferred to 0 (false) without signaling.

For each CP, when the Zero_MVD flag is true, CPMV is set to be the sameas base predictor's corresponding CPMV value. However, when the Zero_MVDflag is false, offset distance index and offset direction index for theCP are signaled in an example. Based on the offset distance index andoffset direction index, the offset distance and the offset direction canbe determined for example based on Tables 1-5. Then, CPMV value isgenerated from the base predictor's corresponding CPMV predictor valuewith the offset distance applied on the offset direction.

In some examples, the number of control points for the current block isdetermined by the affine model type of the base predictor. When the basepredictor uses 4-parameter affine model, the current block uses 2control points. When the base predictor uses 6-parameter affine model,the current block uses 3 control points.

In an example, the base predictor uses four-parameter affine model, andthe parameters that are signaled include a usage flag (e.g.,affine_merge_with_offset usage flag is equal to true), the basepredictor index, zero_MVD flag (false) for a first CP (also referred toas CP0), offset distance index for the first CP, offset direction indexfor the first CP, zero_MVD flag (false) for a second CP (also referredto as CP1), offset distance index for the second CP, and offsetdirection index for the second CP.

In another example, the base predictor uses six-parameter affine model,and the parameters that are signaled include a usage flag (e.g.,affine_merge_with_offset usage flag is equal to true), the basepredictor index, zero_MVD flag (false) for a first CP (also referred toas CP0), offset distance index for the first CP, offset direction indexfor the first CP, zero_MVD flag (false) for a second CP (also referredto as CP1), offset distance index for the second CP, offset directionindex for the second CP, zero_MVD flag (false) for a third CP (alsoreferred to as CP2), offset distance index for the third CP, offsetdirection index for the third CP.

In other embodiment, one set of offset parameters is signaled for allcontrol points. In some examples, the current block's merge flag andaffine_merge_with_offset usage flag are both true. When more than onepredictor candidates are existed to be potentially used for basepredictor, base predictor index is signaled from the encoder side to thedecoder side in an example. In another example, no base predictor indexis signaled, and predefined base predictor index can be used on theencoder side and the decoder side. For the current block, one set ofoffset distance index and offset direction index is signaled. Based onthe offset distance index and the offset direction index, the offsetdistance and the offset direction are determined. Then, the currentblock's CPMV values are generated from the base predictor'scorresponding CPMV predictor values with the offset distance applied onthe offset direction.

In an example, the parameters that are signaled include a usage flag(e.g., affine_merge_with_offset usage flag is equal to true), the basepredictor index, offset distance index for the current block, and offsetdirection index for the current block.

Aspects of the disclosure provide techniques for calculate CPMV values.

In some embodiments, when the inter prediction is uni-prediction, themotion vector difference in the form of applying the offset distance(determined based on the offset distance index decoded from the codedvideo bitstream) on the offset direction (determined based on the offsetdirection index decoded from the coded video bitstream) is used for eachcontrol point predictor. The motion vector difference is then used todetermine the MV value of each control point.

For example, when base predictor is uni-prediction, and the motionvector values of a control point of the base predictor is denoted as MVP(vpx, vpy). When offset distance index and offset direction index aresignaled, the motion vectors of current block's corresponding controlpoints will be calculated using Eq. 5. The distance_offset denotes tothe offset distance value that is determined based on the offsetdistance index. The x_dir_factor and y_dir_factor denotes the offsetdirection factor (e.g, 1 or −1) on x-axis and y-axis respectively, whichare determined based on the offset direction index.MV(vx,vy)=MVP(vpx,vpy)+MV(x_dir_factor×distance_offset,y_dir_factor×distance_offset)  (Eq.5)

In an embodiment, offset mirroring is used for bi-prediction CPMVs. Themotion vector difference (in the form of offset distance and offsetdirection) can be applied, in opposite directions, to motion vectors ofthe control points that refer to a reference picture from the L0 listand to motion vectors of the control points that refer to a referencepicture from the L1 list. When the inter prediction is bi-prediction,the motion vector difference (in the form offset distance and offsetdirection) is applied to the L0 motion vectors (motion vectors thatrefer to a reference picture from the L0 list) of the control pointpredictor to calculate the L0 motion vectors (motion vectors that referto a reference picture from the L0 list) of the control points for thecurrent block; and the motion vector difference is also applied to the Lmotion vectors (motion vectors that refer to a reference picture fromthe L1 list) of the control point predictor but in an opposite directionto calculate the L motion vectors (motion vectors that refer to areference picture from the L1 list) of the control points for thecurrent block. The calculation results will be the MV values of eachcontrol point, on each inter prediction direction.

For example, when base predictor is bi-prediction, and the motion vectorvalues of a control point on L0 (motion vectors that refer to areference picture from the L0 list) is denoted as MVPL0 (v0px, v0py),and the motion vector values of that control point on L1 (motion vectorsthat refer to a reference picture from the L1 list) is denoted as MVPL1(vpx, v1py). When offset distance index and offset direction index aresignaled, the motion vectors of current block's corresponding controlpoints can be calculated using Eq. 6 and Eq. 7:MVL0(v0x,v0y)=MVPL0(v0px,v0py)+MV(x_dir_factor×distance_offset,y_dir_factor×distance_offset)  Eq.6MVL1(v0x,v0y)=MVPL1(v0px,v0py)+MV(−x_dir_factor×distance_offset,−y_dir_factor×distance_offset)  Eq.7

According to another aspect of the disclosure, the CPMV calculationusing offset mirroring is conditionally performed for bi-prediction CPMVcalculation, for example based on the reference picture's location withregard to the current picture.

In an example, when the inter prediction is bi-prediction, the motionvector values of the control points from the L0 list (motion vectorsthat refer to a reference picture from the L0 list) is calculated in thesame way as above, the signaled offset distance is applied on thesignaled offset direction for control point predictor's L0 motion vector(motion vectors that refer to a reference picture from the L0 list).

When the reference pictures from L0 and L1 are on the opposite sides ofthe current picture, to calculate the motion vectors for the controlpoints from L list (motion vectors that refer to a reference picturefrom the L list), the same offset distance with opposite offsetdirection (from the signaled offset direction) is applied for controlpoint predictor's L1 motion vector (motion vectors that refer to areference picture from the L1 list).

When the reference pictures from L0 and L1 are on the same side of thecurrent picture, to calculate the motion vectors for the control pointsfrom L1 list, the same offset distance with same offset direction (asthe signaled offset direction) is applied for control point predictor'sL1 motion vector (motion vectors that refer to a reference picture fromthe L1 list).

It is noted that in some embodiments, the offset distance applied on thereference picture from L1 list is the same as the offset distanceapplied on the reference picture from L0 list; and in some otherembodiments, the offset distance applied on the reference picture fromL1 list is scaled according to the ratio of distance of referencepicture from L0 list to the current picture and distance of referencepicture from L1 list to the current picture.

In an embodiment, the distance offset applied on the reference picturefrom the L1 list is the same as the distance offset applied on thereference picture from the L0 list.

In an example, when base predictor is bi-prediction, and the motionvector values of a control point (of the base predictor) on a referencepicture from the L0 list is denoted as MVPL0 (v0px, v0py), and themotion vector values of that control point (of the base predictor) on areference picture from the L1 list is denoted as MVPL1 (v1px, v1py). Thereference pictures from the L0 list and the L1 list are on the oppositeside of the current picture. When offset distance index and offsetdirection index are signaled, the motion vectors of current block'scorresponding control points can be calculated using Eq. 6 and Eq. 7shown above.

In another embodiment, the offset distance applied on the referencepicture from L1 list is scaled according to the ratio of distance ofreference picture from L0 list to the current picture and distance ofreference picture from L1 list to the current picture.

In an example, when the base predictor is bi-prediction, and the motionvector values of a control point (of the base predictor) on thereference picture from the L0 list is denoted as MVPL0 (v0px, v0py), andthe motion vector values of that control point (of the base predictor)on the reference picture from the L list is denoted as MVPL1 (v1px,v1py). When offset distance index and offset direction index aresignaled, the motion vectors of current block's corresponding controlpoints can be calculated using Eq. 8 and Eq. 9.MVL0(v0x,v0y)=MVPL0(v0px,v0py)+MV(x_dir_factor×distance_offset,y_dir_factor×distance_offset)  (Eq.8)MVL1(v0x,v0y)=MVPL1(v0px,v0py)+MV(x_dir_factor×distance_offset×scaling_factor,y_dir_factor×distance_offset×scaling_factor)  (Eq.9)

The scaling_factor is calculated based on the POC number of currentpicture (denoted as current_POC), the POC number of the referencepicture on the L0 list (denoted as POC_L0), and the POC number of thereference picture on the L1 list (denoted as POC_L1) according to (Eq.10):scaling_factor=(POC_L1−current_POC)/(POC_L0−current_POC)  (Eq. 10)

FIG. 14 shows a flow chart outlining a process (1400) according to anembodiment of the disclosure. The process (1400) can be used in thereconstruction of a block coded in intra mode, so to generate aprediction block for the block under reconstruction. In variousembodiments, the process (1400) are executed by processing circuitry,such as the processing circuitry in the terminal devices (210), (220),(230) and (240), the processing circuitry that performs functions of thevideo encoder (303), the processing circuitry that performs functions ofthe video decoder (310), the processing circuitry that performsfunctions of the video decoder (410), the processing circuitry thatperforms functions of the video encoder (503), and the like. In someembodiments, the process (1400) is implemented in software instructions,thus when the processing circuitry executes the software instructions,the processing circuitry performs the process (1400). The process startsat (S1401) and proceeds to (S1410).

At (S1410), prediction information of a current block in a currentpicture is decoded from a coded video bitstream. The predictioninformation is indicative of an affine merge mode with offset.

At (S1420), in response to the affine merge mode with offset, a set ofoffset parameters is decoded from the coded video bitstream. Based onthe set of offset parameters, a motion vector difference is determined.In some examples, the motion vector different is used in the form ofapplying an offset distance to an offset direction.

At (S1430), the motion vector difference is applied to first motionvectors of multiple control points from a base predictor of the currentblock to calculate second motion vectors at corresponding multiplecontrol points of the current block.

At (S1440), parameters of an affine model are determined based on thesecond motion vectors at the corresponding multiple control points ofthe current block.

At (S1450), samples of the current block are reconstructed based on theaffine model. For example, for a sample of the current block, a motionvector at the sample is calculated according to the affine model. Thus,in an example, the sample is constructed based on a reference sample ina reference picture that is pointed by the motion vector. Then, theprocess proceeds to (S1499) and terminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 15 shows a computersystem (1500) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 15 for computer system (1500) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1500).

Computer system (1500) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1501), mouse (1502), trackpad (1503), touchscreen (1510), data-glove (not shown), joystick (1505), microphone(1506), scanner (1507), camera (1508).

Computer system (1500) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1510), data-glove (not shown), or joystick (1505), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1509), headphones(not depicted)), visual output devices (such as screens (1510) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability-some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1500) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1520) with CD/DVD or the like media (1521), thumb-drive (1522),removable hard drive or solid state drive (1523), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1500) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1549) (such as, for example USB ports of thecomputer system (1500)); others are commonly integrated into the core ofthe computer system (1500) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1500) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1540) of thecomputer system (1500).

The core (1540) can include one or more Central Processing Units (CPU)(1541), Graphics Processing Units (GPU)(1542), specialized programmableprocessing units in the form of Field Programmable Gate Areas(FPGA)(1543), hardware accelerators for certain tasks (1544), and soforth. These devices, along with Read-only memory (ROM)(1545),Random-access memory (1546), internal mass storage such as internalnon-user accessible hard drives. SSDs, and the like (1547), may beconnected through a system bus (1548). In some computer systems, thesystem bus (1548) can be accessible in the form of one or more physicalplugs to enable extensions by additional CPUs, GPU, and the like. Theperipheral devices can be attached either directly to the core's systembus (1548), or through a peripheral bus (1549). Architectures for aperipheral bus include PCI, USB, and the like.

CPUs (1541), GPUs (1542), FPGAs (1543), and accelerators (1544) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1545) or RAM (1546). Transitional data can be also be stored in RAM(1546), whereas permanent data can be stored for example, in theinternal mass storage (1547). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1541), GPU (1542), massstorage (1547), ROM (1545), RAM (1546), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1500), and specifically the core (1540) can providefunctionality as a result of processor(s)(including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1540) that are of non-transitorynature, such as core-internal mass storage (1547) or ROM (1545). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1540). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1540) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1546) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1544)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding prediction information of a current block in acurrent picture from a coded video bitstream, the prediction informationincluding a usage flag indicative of an affine merge mode with offset;decoding, from the coded video bitstream, offset parameters defining oneor more motion vector differences having a distance and having adirection; decoding, from the coded video bitstream, a zero motionvector difference flag for each of one or more control points ofmultiple control points of a base predictor, the zero motion vectordifference flag indicating whether offset parameters for the respectivecontrol point are provided in the coded video bitstream; determining acorresponding motion vector difference for each of the multiple controlpoints of the base predictor based on at least one of the offsetparameters and the zero motion vector difference flag; determining acorresponding motion vector for each of the multiple control points ofthe base predictor based on the determined corresponding motion vectordifference for the respective control point; and reconstructing at leasta sample of the current block according to the determined correspondingmotion vector for each of the multiple control points.
 2. The method ofclaim 1, further comprising: determining a number of base predictorcandidates based on the decoded prediction information; and in responseto a determination that the number of base predictor candidates isgreater than one, decoding, from the coded video bitstream, a basepredictor index indicating the base predictor.
 3. The method of claim 1,further comprising: determining a number of base predictor candidatesbased on a predefined value; and in response to a determination that thenumber of base predictor candidates is greater than one, decoding, fromthe coded video bitstream, a base predictor index indicating the basepredictor.
 4. The method of claim 1, wherein the offset parametersinclude one or more offset direction indexes and one or more offsetdistance indexes, one of the one or more offset direction indexes andone of the one or more offset distance indexes defining one of the oneor more motion vector differences.
 5. The method of claim 4, whereineach of the one or more offset direction indexes refers to a predefinedmapping table defining a correspondence between each of the one or moreoffset direction indexes and a direction along at least one of an x axisand a y axis.
 6. The method of claim 4, wherein each of the one or moreoffset distance indexes refers to a predefined mapping table defining acorrespondence between each of the one or more offset distance indexesand a distance measured in pixels.
 7. The method of claim 4, wherein theoffset parameters include a corresponding offset direction index and acorresponding offset distance index defining a corresponding motionvector difference for at least one of the multiple control points. 8.The method of claim 1, further comprising determining a number of themultiple control points based on an affine model type of the basepredictor.
 9. The method of claim 1, wherein the determining thecorresponding motion vector for each of the multiple control pointscomprises for a first control point of the multiple control points thatrefers to a first reference picture, applying the determined motionvector difference corresponding to the first control point to determinethe corresponding motion vector for the first control point; and for asecond control point of the multiple control points that refers to asecond reference picture, applying a mirror of the determined motionvector difference corresponding to the second control point to determinethe corresponding motion vector for the second control point.
 10. Anapparatus for video decoding, comprising: processing circuitryconfigured to: decode prediction information of a current block in acurrent picture from a coded video bitstream, the prediction informationincluding a usage flag indicative of an affine merge mode with offset;decode, from the coded video bitstream, offset parameters defining oneor more motion vector differences having a distance and having adirection; decode, from the coded video bitstream, a zero motion vectordifference flag for each of one or more control points of multiplecontrol points of a base predictor, the zero motion vector differenceflag indicating whether offset parameters for the respective controlpoint are provided in the coded video bitstream; determine acorresponding motion vector difference for each of the multiple controlpoints of the base predictor based on at least one of the offsetparameters and the zero motion vector difference flag; determine acorresponding motion vector for each of the multiple control points ofthe base predictor based on the determined corresponding motion vectordifference for the respective control point; and reconstruct at least asample of the current block according to the determined correspondingmotion vector for each of the multiple control points.
 11. The apparatusof claim 10, wherein the processing circuitry is further configured to:determine a number of base predictor candidates based on the decodedprediction information; and in response to a determination that thenumber of base predictor candidates is greater than one, decode, fromthe coded video bitstream, a base predictor index indicating the basepredictor.
 12. The apparatus of claim 10, wherein the processingcircuitry is further configured to: determine a number of base predictorcandidates based on a predefined value; and in response to adetermination that the number of base predictor candidates is greaterthan one, decode, from the coded video bitstream, a base predictor indexindicating the base predictor.
 13. The apparatus of claim 10, whereinthe offset parameters include one or more offset direction indexes andone or more offset distance indexes, one of the one or more offsetdirection indexes and one of the one or more offset distance indexesdefining one of the one or more motion vector differences.
 14. Theapparatus of claim 13, wherein each of the one or more offset directionindexes refers to a predefined mapping table defining a correspondencebetween each of the one or more offset direction indexes and a directionalong at least one of an x axis and a y axis.
 15. The apparatus of claim13, wherein each of the one or more offset distance indexes refers to apredefined mapping table defining a correspondence between each of theone or more offset distance indexes and a distance measured in pixels.16. The apparatus of claim 13, wherein the offset parameters include acorresponding offset direction index and a corresponding offset distanceindex defining a corresponding motion vector difference for each of themultiple control points.
 17. The apparatus of claim 10, furthercomprising determining a number of the multiple control points based onan affine model type of the base predictor.
 18. The apparatus of claim9, wherein the processing circuitry determines the corresponding motionvector for each of the multiple control points by, for a first controlpoint of the multiple control points that refers to a first referencepicture, applying the determined motion vector difference correspondingto the first control point to determine the corresponding motion vectorfor the first control point; and for a second control point of themultiple control points that refers to a second reference picture,applying a mirror of the determined motion vector differencecorresponding to the second control point to determine the correspondingmotion vector for the second control point.
 19. A non-transitorycomputer-readable medium storing instructions which, when executed by acomputer for video decoding, cause the computer to perform: decodingprediction information of a current block in a current picture from acoded video bitstream, the prediction information including a usage flagindicative of an affine merge mode with offset; decoding, from the codedvideo bitstream, offset parameters defining one or more motion vectordifferences having a distance and having a direction; decoding, from thecoded video bitstream, a zero motion vector difference flag for each ofone or more control points of multiple control points of a basepredictor, the zero motion vector difference flag indicating whetheroffset parameters for the respective control point are provided in thecoded video bitstream; determining a corresponding motion vectordifference for each of the multiple control points of the base predictorbased on at least one of the offset parameters and the zero motionvector difference flag; determining a corresponding motion vector foreach of the multiple control points of the base predictor based on thedetermined corresponding motion vector difference for the respectivecontrol point; and reconstructing at least a sample of the current blockaccording to the determined corresponding motion vector for each of themultiple control points.